Originally Posted by fletch

A hood won't actually help much if the sun is actually in shot.

The real use of a hood is stopping light entering the lens that is not part of the composition. This light hits the lens at funny angles and bounces arround inside causing funky affects such as flare, and also affecting overall contrast of the image.

So moral of the story, there really is no downside to using a (well made) lens hood, just use it all of the time. However it won't magic your pictures better or stop shooting into the sun being difficult and causing lens flare.